What does making a song "wider" mean?

It is the sense that the sound occupies more space to the sides, more immersive.

Can it sound odd in mono?

If you overdo it, yes. That is why the tool shows correlation so you can protect compatibility.

Ideally the bass stays centered; you can combine it with the bass-to-mono tool.

Online audio tool

Give your mix a wider, more immersive feel without losing the bass or breaking compatibility when it plays in mono.

Target search: widen stereo of a song

Upload your song or mix.

Set how much stereo width you want.

Check the goniometer and correlation.

Download the wider version.